Header boxes for the heat exchange industry are typically constructed from steel plate welded to form a box. Front and back plates are drilled to accommodate heat exchange tubes. The welding and subsequent annealing processes typically distort the front and back plates. After the header box is welded further machining is required to finish the holes. This includes boring, spot facing, grooving, chamfering and tapping in order to accept a tube on one side and a plug on the other side. The welded header boxes can be machined manually by radial drilling using high speed steel tools which is very labor intensive. As an example a header box with 540 holes typically takes twelve hours to machine on a radial drill.
CNC machines using carbide tools can work much faster than a manual radial drill but require accurate location information for each hole. Even if the holes were originally bored on a CNC machine, because the welding process distorts the plates, the hole locations must be a re-determined. This is typically done by probing each hole with a ruby tipped measurement probe. Probing is performed on the CNC machine but is typically very slow, it requires positioning the delicate probe tip inside each hole and moving it in four directions until the probe contacts the side of the hole, taking care not to damage the probe tip. The probe must be centered in each hole and the X axis and Y axis limits measured. This can add five hours to the machining time for a 540 hall header box, negating much of the time savings in using a CNC machine.
Accordingly, a method and system for quickly and accurately determining the location of holes in a welded header box, remains highly desirable.